1. Field of the Invention
The present invention relates to tube sizing devices, and more particularly, to a method and apparatus for sizing flat, multi-void, extruded tubes for automotive heat exchangers.
2. Description of the Invention
Conventional aluminum heat exchangers were manufactured with relatively long pieces of multi-void tubing (i.e., tubing in which the interior space is divided into multiple longitudinal voids by a plurality of longitudinal webs), and then bent into a serpentine configuration. Although these serpentine heat exchangers were satisfactory with fluorocarbon refrigerants R-12 and R-22, they did not perform well with CFC-134a.
A new configuration of condenser core thus was developed for use with CFC-134a: the micro-multi-void extrusion. These micro-extrusions (referred to herein as "micro-extruded tubes") are cut to length and assembled to make up a series of parallel paths for the refrigerant to flow through.
However, prior art extrusion technology originally could not produce a tube with micro-multi-voids to the extremely tight tolerances required in the manufacture of parallel-flow condenser coils. The prior art thus developed tube sizing technology which could control the thickness of the micro-extruded tubes. Currently, there are two methods in use in the art. The first method is rolling, in which the microtube is passed through a series of rollers which reform the material to a pre-determined size. The roller sizing machines which are used in the rolling method generally are fed microtubes from a coil of material. The rolling method is very slow and costly to perform.
U.S. Pat. No. 5,058,266 to Knoll is illustrative of the rolling method. As disclosed by Knoll, the tubes as initially extruded have an oval shape with two transverse webs connecting the long sides of the oval. The tube is then rolled under pressure, flattening the oval sides and comprising and bending the transverse webs. In addition, there is disclosed a similar rolling operation for tubes having one or two internal fins which initially do not extend entirely to the far wall of the tube. However, upon rolling, the two sides of the tube are flattened, and the internal fins do not contact the far wall of the tube.
A second method in use in the art is a compression method, in which a die is sized to hold a single tube. The tube is placed in the die and compressed to reach the desired size. The compression method also is very slow and costly to perform, because it treats only a single tube at a time.
U.S. Pat. Nos. 3,776,018 and 3,662,582 to French are illustrative of the compression method. As disclosed by French, heat exchanger tubing of an oval cross section with two parallel opposite sides is made by compressing tubes initially having a circular cross section and short internal fins. The internal fins act as spacers to prevent excessive compression of the tube. After the compression step, the walls of the tube are partially separated by fluid pressure.
Compression has also been used generally for sizing single tube blanks, both for heat exchangers and other applications.
In U.S. Pat. Nos. 4,829,803 and 4,744,237 to Cudini, a box-like frame member is formed by compressing a tube blank into a square shape between two matching dies. Each die has a rectangular groove in it, such that when the two dies are brought together they compress a tube of circular or similar cross section into a rectangular cross section shape.
In U.S. Pat. No. 4,527,411 to Shinosaki et al., the circular tube is heated to a temperature of 550.degree. to 1250.degree. C. and compressed within a box-like form having three sides by the application of pressure through a compressing side.
In U.S. Pat. No. 4,204,309 to Lefrancois, a process of compressing hollow bead rings for the beads of pneumatic tires. The beads have an oval or diamond-shaped cross section, with a web extending from one of the longer sides partially across the cross sectional distance. The opposite wall of the tube may have a mating surface into which the transverse webs fit at the end of the compression step. However, no particular compression method is specified.
According to the above-discussed references, only one tube is sized at a time in a die that has been designed to hold only one tube during the application of the sizing pressure. Thus, the method is also relatively slow and expensive. It is the solution to these and others objects to which the present invention is directed.